In fabricating integrated circuit devices, one or more conductive layers, typically a metal such as aluminum or an aluminum alloy, is deposited and subsequently patterned to provide contacts and/or interconnections between various circuit components. Such processing typically comprises depositing a photoresist on the metal layer, exposing the photoresist to a light pattern and then developing to form the pattern. The patterned photoresist is then employed as a mask through which the underlying metal layer is selectively etched, as by high density plasma etching employing a chlorine-containing gas. The remaining photoresist is then removed leaving the desired metal pattern typically comprising a plurality of closely spaced metal lines. Metal, such as aluminum, exhibits a high reflectivity. Accordingly, conventional practices comprise depositing an anti-reflective coating on the metal layer, prior to photolithographic processing. The anti-reflective coating, which typically comprises titanium nitride, reduces interference effects and diffuse scattering. See, for example, Abernathey et al., U.S. Pat. No. 5,219,788, wherein various conventional anti-reflective materials are disclosed.
A conventional method of forming a conductive metal pattern is disclosed in Arnold, III et al., U.S. Pat. No. 4,820,611 and comprises, as shown in FIG. 1A, depositing metal layer 12, such as aluminum or an aluminum alloy, on a portion of an integrated circuit 10, and depositing an anti-reflective coating 16, notably titanium nitride, on metal layer 12. A photoresist layer 14 is formed on anti-reflective layer 16. A mask 20 containing light apertures 22 is positioned over photoresist layer 14. Light rays, indicated by arrows 18, are passed through apertures 22 exposing selected areas of photoresist layer 14. After development, the exposed areas of photoresist layer 14 and the underlying portions of anti-reflective layer 16 are removed as shown in FIG. 1B. Subsequently, metal layer 12 is etched to form a conductive pattern, such as an interconnect pattern, and photoresist mask 14 removed, as depicted in FIG. 1C. Anti-reflective coating 16 on the remaining metal pattern 12 can be retained or removed.
Conventional practices consistently comprise the deposition of an anti-reflective coating comprising a material which is dissimilar to the material of the underlying conductive layer on which the anti-reflective coating is deposited. The use of an anti-reflective layer comprising a material different from the material of the conductive layer disadvantageously involves costly processing in terms of additional materials, manipulative steps, equipment and production time. In fact, in a physical vapor deposition system, titanium nitride deposition is the rate limiting step.
Moreover, the ever increasing demands for semiconductor devices containing conductive patterns having increasingly narrower line widths and increasingly narrower interwiring spacings therebetween generate acute problems with respect to current photolithographic capabilities. Such demands for increased miniaturization necessitate the use of deep UV photo-imaging or image-developing operations requiring photoresist materials which are incompatible with titanium nitride. For example, Abernathey et al. provide a barrier layer of silicon on a titanium nitride anti-reflective coating to avoid the generation of defects attendant upon depositing an acid-catalyzed photoresist on a titanium nitride anti-reflective layer.
Accordingly, there exists a need for photolithographic technology which avoids the use of an anti-reflective film of a material different from that of the underlying conductive layer while satisfying the demands for increasingly smaller conductive line widths and smaller interwiring spacings.